class Solution {
    public boolean isSymmetric(TreeNode root) {
        if(root==null)
            return true;
        return isSymmetric(root.left,root.right);
    }
    public boolean isSymmetric(TreeNode left,TreeNode right){
        if(left==null&&right==null)
            return true;
        if(left==null||right==null)
            return false;
        return left.val==right.val&&isSymmetric(left.left,right.right)&&isSymmetric(left.right,right.left);
    }
}